bpo-27129: Use instruction offsets, not byte offsets, in bytecode and internally. (GH-25069)

* Use instruction offset, rather than bytecode offset. Streamlines interpreter dispatch a bit, and removes most EXTENDED_ARGs for jumps.

* Change some uses of PyCode_Addr2Line to PyFrame_GetLineNumber

Python/compile.c

@@ -6398,7 +6398,6 @@ assemble_jump_offsets(struct assembler *a, struct compiler *c)
                     if (is_relative_jump(instr)) {
                         instr->i_oparg -= bsize;
                     }
-                    instr->i_oparg *= sizeof(_Py_CODEUNIT);
                     if (instrsize(instr->i_oparg) != isize) {
                         extended_arg_recompile = 1;
                     }